directshow - How to detect webcam plug / unplug? - directshow

Question

Is there a simple way with DirectShow to detect if the webcam is plugged in (USB), or if someone has unplugged it (and then poll or search for it)?
I have seen code for Microsoft Media Foundation, but it is complex and Media Foundation isn't installable on < Vista, afaik.
Thx, WW

Answer 1

i use a WMI event watcher looking for the PID in the property string (some cameras may fire the events twice depending on drivers). here is a VB.Net example:
Dim CamEventWatcher As ManagementEventWatcher
Public Delegate Sub SetMessageCallback(ByVal [_Msg] As Boolean)
Private Sub MessageCallback(ByVal _Msg As Boolean)
If (_Msg) Then
'cam connected
Else
'camera removed
End If
End Sub
Private Sub RemoveCameraUSBHandler()
Try
If Not CamEventWatcher Is Nothing Then
CamEventWatcher.Stop()
End If
Catch ex As Exception
End Try
End Sub
Private Sub AddCameraUSBHandler()
Dim q As WqlEventQuery
Dim scope As ManagementScope = New ManagementScope("root\CIMV2")
scope.Options.EnablePrivileges = True
Try
q = New WqlEventQuery()
q.EventClassName = "__InstanceOperationEvent"
q.WithinInterval = New TimeSpan(0, 0, 1)
q.Condition = "TargetInstance ISA 'Win32_USBControllerdevice'"
CamEventWatcher = New ManagementEventWatcher(scope, q)
AddHandler CamEventWatcher.EventArrived, AddressOf CamUSBEvent
CamEventWatcher.Start()
Catch ex As Exception
End Try
End Sub
Private iCreatedFired As Integer = 0
Private iRemovedFired As Integer = 0
Public Sub CamUSBEvent(ByVal sender As System.Object, ByVal e As EventArrivedEventArgs)
If e.NewEvent.ClassPath.ClassName = "__InstanceCreationEvent" Then
Dim sAntecedent As String
Dim sDependent As String
sAntecedent = e.NewEvent.Properties("TargetInstance").Value.Properties("Antecedent").Value.ToString() + ControlChars.CrLf
sDependent = e.NewEvent.Properties("TargetInstance").Value.Properties("Dependent").Value.ToString() + ControlChars.CrLf
If sDependent.Contains(CAM_DEV_ID) Then
iCreatedFired += 1
If (iCreatedFired = 1) Then
e.NewEvent.Dispose()
Return
End If
iCreatedFired = 0
iRemovedFired = 0
Dim _delegate As New SetMessageCallback(AddressOf MessageCallback)
Me.Invoke(_delegate, New Object() {True})
End If
ElseIf e.NewEvent.ClassPath.ClassName = "__InstanceDeletionEvent" Then
Dim sAntecedent As String
Dim sDependent As String
sAntecedent = e.NewEvent.Properties("TargetInstance").Value.Properties("Antecedent").Value.ToString() + ControlChars.CrLf
sDependent = e.NewEvent.Properties("TargetInstance").Value.Properties("Dependent").Value.ToString() + ControlChars.CrLf
If sDependent.Contains(CAM_DEV_ID) Then
iRemovedFired += 1
If (iRemovedFired = 1) Then
e.NewEvent.Dispose()
Return
End If
iCreatedFired = 0
iRemovedFired = 0
Dim _delegate As New SetMessageCallback(AddressOf MessageCallback)
Me.Invoke(_delegate, New Object() {False})
End If
End If
e.NewEvent.Dispose()
End Sub